1. Field of the Invention
This invention relates to the structure of an improved industrial robot associated with cables used for supplying electric power or transmitting electrical signals, and with ducts and other pipelines used for conveying air, coolants, or other fluids.
2. Description of the Related Art
In general, industrial robots (hereinafter referred to as robots) are equipped with motors to drive the robot axis, electrical cables for supplying electric power to or sending and receiving electrical signals to and from machining tools and, small cameras mounted on the robots, and ducts or other pipelines for conveying air, coolants, or other fluids.
As robots ordinarily move in conjunction with such actions as turning, extending, or retracting, in installing the cables and ducts (hereinafter both cables and ducts are referred to as "cable(s)"), care must be taken so that the installed cables do not inhibit robot movement, and so that the cables are not subjected to excessive tension, twisting, or tangling by the movement of the robot. In particular, when the range of a robot's turning movement is made large (360.degree. for example), cables tend to get wrapped up and damaged by excessive tension. In many cases, therefore, it becomes inevitable to limit the range of a robot's turning movement with reluctance.
In order to avoid such limitations, there is a known technique with which through-holes are opened in the centers of the speed reducers with which the drive units of robot axis are equipped, and cables are run through those through-holes (see Japanese Patent Application, Laid-Open H7-108485).
When such a cable installation technique is employed in each robot axis, one naturally would expect that cable interference with robot axis movements, particularly with turning movements, would be reduced, and that limitations on the range of movement of robot axis, particularly the range of turning movement, would be greatly relaxed.
There is a problem, however, in that the structure of the speed reducer mechanism where through-holes are provided in the center becomes complex because of the unavoidable necessity of providing a bearing mechanism for mechanical input and output at the periphery thereof, away from the center thereof. For this reason, if such a bearing mechanism is employed in all of the robot axes in order to avoid cable interference when the robot axis make a turning movement, the entire structure becomes complex, and the overall cost rises.